Fuel pumps used in fuel injection equipment of internal combustion engines use a cam-follower to follow a cam profile and translate rotational movement into reciprocating movement displacing the piston compressing fuel in a compression chamber.
A return spring mechanism supplies the required force to keep the cam and the cam-follower in a continuous contact.
The fuel is compressed by the displacement of the piston and reaches a high pressure level that can be 3000 bar. The piston is guided in the hydraulic head bore with a small and precisely controlled clearance and, some of the fuel can leak thought this clearance to the follower side during the pumping stage due to the pressure differences between the compression chamber just above the piston and the cam-follower side. In the oil lubricated fuel pump systems the cam-follower intersection is lubricated by engine oil.
The most critical problem of such oil lubricated fuel pump systems is separating the leaked fuel from the lubrication oil. If the lubrication oil and the fuel become mixed it can lead to engine damage. If a high quantity of oil is present in the fuel then this can lead for instance to injector damages or damages to particulate filters. Similarly a high level of fuel in the oil will compromise the oil lubrication thereby increasing engine wear.
The prior art is to separate the fuel and the lubrication oil using a matched length and/or a seal on the piston. However neither option is capable to separate the two liquids completely due to the movement of the piston.